The use of optical fibers for communications is growing at an unprecedented rate. An optical fiber comprises a glass fiber which is drawn from a preform and which has an uncoated diameter of about 125 microns and a coated diameter of about 250 microns.
Subsequently, the drawn optical fiber may be marked for purposes of identification in the field. Identification becomes necessary inasmuch as some cables which are shipped to the field are not preconnectorized in the factory. Also, if cables in the field are damaged such as by inadvertent impact with construction equipment, it becomes necessary to splice optical fibers to replace the damaged portions.
Generally, an optical fiber is identified by a marking which is provided on the outer surface of the coated fiber. The marking usually comprises inked indicia which are spaced along the length of the optical fiber. Typically, the markings are about 0.25 inch long and spaced apart about 0.25 inch. The ink which is used to mark the fibers typically is a permanent ink having a viscosity of about 3-5 cps at ambient temperature. Each inked indicium is applied about only two thirds of the periphery of each optical fiber. This is helpful to particular tests of the marked fiber which are made when it is wrapped about a mandrel, for example.
As can be imagined, the prior art includes arrangements for marking elongated strand material and for marking optical fibers. One such arrangement for elongated strand material is shown in U.S. Pat. No. 3,176,650 which issued to H. L. Woellner on Apr. 6, 1965. In that apparatus, a disc is mounted for rotation about an axis which is angled to the path of travel of an advancing elongated strand material. As the disc turns, a marking medium is flowed radially outwardly to ports to allow the marking medium to be slung into contact with the elongated strand material.
As for optical fibers, it has been customary to advance a fiber across and in engagement with a wick to which a marking ink is supplied. A cam is used to engage the moving optical fiber and intermittently to disengage the optical fiber from the wick to thereby provide spaced indicia along the fiber. Problems have occurred in the use of such an arrangement. The indicia, typically in the form of dashes, are not uniform and it is difficult to synchronize the movement of the cam with the line speed of the optical fiber.
In another commercially available apparatus, a grease-like ink is pumped upwardly into an application chamber through which an optical fiber is being advanced into engagement with an applicator wheel. It has been found that this arrangement requires a thorough cleaning afer it had been used to mark about 1000 meters of fiber. Also, there is no provision for overflow of the ink. Consequently, it is difficult to control the quantity of ink in the application chamber. If there is too much ink, the applicator wheel becomes clogged; if there is too little, it is starved.
Another desired capability of an inking apparatus is that its geometry permits a plurality of such apparatus to be arranged side-by-side to ink a plurality of optical fibers moving in parallel paths prior to the assembly of the fibers into a ribbon. Many commercially available marking arrangements are too bulky to permit such side-by-side use to mark optical fibers which are moving along closely spaced paths.
Clearly, there is a need for methods and apparatus for marking optical fibers in a uniform manner to facilitate field identification. The sought-after apparatus should be one which can be placed side-by-side with other identical apparatus to mark a plurality of optical fibers being advanced side-by-side in closely spaced relation to one another.